1. Field of the Invention
This invention relates to a method of starting up a generating plant of the kind having a gas turbine driven by combustion gases from a carbon pressure reactor in which the pressure reactor is initially operated with extraneous air from a starting compressor and the starting fuel gas produced used to accelerate an expansion turbine to drive a final compressor. After production of a sufficient amount of fuel gas to put a combustion chamber and the gas turbine into operation, the combustion chamber is coupled to the expansion turbine. The gas turbine drives a primary air compressor so that the supply of extraneous air may be cut off.
Moreover, the invention relates to a generating plant to which this method of starting can be applied.
2. Description of the Prior Art
Plants of the foregoing type run with a relatively high degree of efficiency because relatively higher inlet temperatures are possible in a gas turbine than in steam turbines. The plant is also cheaper. The gas turbine is usually combined with a steam turbine in a power station block. The steam turbine is operated with a steam boiler which is connected at the outlet side of the combustion chamber in which the gas is produced to operate the gas turbine. This gas is formed by combustion of gas or oil. The fuel gas of the combustion chamber is supplied by a pressure reactor if coal is used as fuel. This gas is thus produced in a pressure reactor from the inserted coal, from steam and from correspondingly compressed combustion air.
Known plants of this type are usually used for supplying peak loads. They must be able, therefore, to be started up frequently and quickly. Since the combustion air required for starting up the carbon pressure reaction cannot be supplied by the primary compressor, because the gas turbine is not yet in operation then, extraneous or auxiliary air is used for this purpose.
In known plants of this type an air cell and a starting turbine driven by a motor are used. The air cell is designed so that it can supply the necessary combustion air for starting the pressure reactor for a period of about 15 minutes. The combustion chamber is put into operation with ignition oil so that the gas turbine can start and drive the primary compressor. The pressure reactor is started with the extraneous air from the cell. The starting gas arising therefrom is directed away upstream of the expansion turbine and is burned off. This is necessary because the expansion turbine cannot be sufficiently cooled when starting the pressure reactor, but drag losses arise due to the plant members coupled to the expansion turbine, i.e., a pony motor with its gear and the final compressor.
When the pressure reactor produces about 20% of the fuel gas, gas valves upstream of the combustion chamber are opened. As a result the expansion turbine begins to rotate. Only then is the pony motor of the expansion turbine switched on, said motor having to drive both the turbine and the final compressor. Only after the required combustion air is produced by the plant itself, can the supply of extraneous air be switched off.
Such plant has a series of grave disadvantages. The combustion chamber must be equipped for combustion of pressure gas and of light oil. This considerably increases the cost of this part of the plant. Also maloperation can arise when starting up the plant. For example if the ignition burner in the combustion chamber fails then the gas turbine cannot be set into operation in time, with the result that the air cell is prematurely exhausted. Since loading the cell takes up approximately 3 hours, power supply fails during this time. Moreover, the relatively high consumption of light oil, which arises when starting the plant is of course unfavorable.
Since in the known plant, the expansion turbine, the final compressor and the drive motor are mounted on the same shaft, the turbine must be dragged along when starting the final compressor by means of the motor, whereby friction losses (pump losses) and consequent high heat production occur in the expansion turbine. For this reason the expansion turbine must be cooled with gas from the pressure reactor. Such gas is, however, not available in sufficient quantity in the first starting phase. Thus it is essential to bring the pressure reactor on to producing fuel gas in an unduly short time in order to avoid overheating the expansion turbine.
This quick acceleration of the pressure reactor is disadvantageous to its operation. On the one hand regulation of the pressure reactor in this case may be poorly controlled. On the other hand the quality of the gas deteriorates, excessive fluctuations in quality and also carry over of dust occur. Damage often occurs in the pressure reactor due to a sudden local increase in temperature and to uncontrollable dispersion of the surface steam.